The present invention relates to fluid flow machines in general, and more particularly to improvements in fluid flow machines of the type wherein an axial piston pump is operated by an electromagnet, especially to improvements in fluid flow machines wherein the axial piston pump is a diaphragm pump.
It is already known to construct a fluid flow machine, wherein a diaphragm pump is operated by an electromagnet, in such a way that the electromagnet can be energized by two different energizing devices. Reference may be had to fluid flow machines which are distributed by the assignee of the present application under the designation "ProMinet"(trademark). The arrangement is such that the electromagnet can be energized by a timer circuit (internal operation) or by a pulse generator (external operation) which is connectable to the fluid flow machine by a separable coupling including a plug and a socket for the plug. The extent or reciprocatory movement of the armature of the electromagnet determines the quantity of fluid which is conveyed by the pump in response to each energization of the electromagnet. The stroke of the armature is adjustable so that an attendant can select the quantity of fluid which is conveyed by the pump whenever the electromagnet is energized so that its armature performs a forward and a return stroke. When the fluid flow machine is set for internal operation, the timer circuit energizes the electromagnet at a selected frequency so that the pump delivers a constant (but variable) quantity of fluid per unit of time. If the fluid flow machine is converted for external operation, the aforementioned pulse generator can initiate the energization of the electromagnet at a frequency which is regular or irregular, e.g., as a function of one or more variable parameters, depending on the intended use of the fluid which is conveyed by the pump. For example, the pulse generator can energize the electromagnet at a frequency which is a function of the rate of fluid flow in a pipe wherein such rate is monitored by a flow measuring device serving to transmit signals to the pulse generator. The means for converting the fluid flow machine from internal operation to external operation or vice versa comprises a selector switch which is actuated by the person in charge.
A drawback of the just discussed fluid flow machine is that the conversion from external operation to internal operation is not foolproof. For example, it can happen that, when an attendant wishes to shift from internal operation to external operation, the attendant properly attaches the male connector (plug) of the aforementioned coupling to the female connector (socket) but the attendant forgets to change the position of the selector switch so that the electromagnet continues to be energized at a frequency which is determined by the timer circuit rather than at a frequency which is dependent on the pulse generator and the associated flow measuring device. Consequently, the body of liquid whose flow is measured receives metered quantities of a fluid medium at a frequency which is not dependent on the rate of liquid flow past the measuring device. This can create serious problems, especially if the liquid whose flow is measured is drinking water and the pump is designed to admit thereto certain chemicals which, if ingested in excessive quantities, can be harmful to the consumers.